1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus which have the electrophotographic photosensitive member.
2. Related Background Art
Various systems such as an electrophotographic system, a thermal transfer system and an ink-jet recording system have been employed in image forming apparatus. Of these, image forming apparatus employing the electrophotographic system are superior to image forming apparatus employing the other systems, in view of higher speed, higher image quality and less noise, and are employed in many copying machines and printers.
Image formation by the electrophotographic system is performed by a process in which the surface of an electrophotographic photosensitive member is electrostatically charged, the surface of the electrophotographic photosensitive member thus charged is exposed to exposure light to form an electrostatic latent image on the surface of the electrophotographic photosensitive member, this electrostatic latent image is developed with a toner (a developer) to form a toner image on the surface of the electrophotographic photosensitive member, and this toner image is transferred from the surface of the electrophotographic photosensitive member to a transfer material such as paper.
At present, laser light is widely used as the above exposure light. Where laser light is used as exposure light, the electrostatic latent image formed on the surface of the electrophotographic photosensitive member is formed as a digital electrostatic latent image (a digital latent image).
As the electrophotographic photosensitive member, widely used is an electrophotographic photosensitive member (an organic electrophotographic photosensitive member) having a photosensitive layer containing an organic charge-generating material and a charge-transporting material. As such a photosensitive layer, from the viewpoint of durability, what is prevalent is one having layer configuration of a multi-layer type (regular-layer type) in which a charge generation layer containing a charge-generating material and a charge transport layer containing a charge-transporting material are superposed in this order from the support side.
In these days, the progress of electrophotographic technique is remarkable, and electrophotographic photosensitive members are also required to have high performance. In particular, the performance that deals with higher image quality has become strongly demanded.
As the reason that such higher image quality is demanded, it is cited that the electrophotographic technique has, in virtue of their on-demand availability, advanced into the market that has belonged to printing techniques such as offset printing and screen printing. Accordingly, a high image quality on the level of that in printing techniques is demanded in respect of reproducibility of small-point characters and photographic images, in particular, reproducibility of halftone images.
However, in the printing techniques such as offset printing and screen printing, the shape of a plate is faithfully reproduced, whereas in the electrophotographic technique, especially when laser light is used as exposure light, there is a problem concerning deterioration of dot reproducibility, i.e., a problem such that not only dots on the electrophotographic photosensitive member surface but dots on reproduced images are inevitably enlarged as compared with laser beam spots. It is considered that the dots of electrostatic latent images formed on the surface of the electrophotographic photosensitive member are shallower and broader in their three-dimensional shapes. Also, this problem is remarkable where the dots are contiguous to each other.
As a technique by which the dot reproducibility is improved, an induction photosensitive member is disclosed in, e.g., Japanese Patent Applications Laid-open No. H01-169454, No. H03-287171 and No. H09-096914, in which its potential does not attenuate until reaching a certain amount of exposure light and steep attenuation of potential takes place when exceeding that amount of exposure light.